Combine yellow and brown mustard seeds, vinegar and 1-1/2 cups water in a large bowl; cover and let stand at room temp until the liquid is mostly absorbed, at least 6 hrs (or up to 24 hrs)
Preheat oven to 400 deg F. Rub of excess papery skin from garlic. Slice the tip off the head, exposing the cloves. Drizzle oil wrap in foil and roast for 40 - 60 mins. When the garlic is cool enough to handle squeeze out the cloves.
In food processor grind mustard seed mixture and garlic in two batches put into bowl. Stir in the maple syrup and salt.
Spoon the mixture into air tight containers and refrigerate.